Large scale production of oxidized graphene

ABSTRACT

Embodiments described herein relate generally to the large scale production of functionalized graphene. In some embodiments, a method for producing functionalized graphene includes combining a crystalline graphite with a first electrolyte solution that includes at least one of a metal hydroxide salt, an oxidizer, and a surfactant. The crystalline graphite is then milled in the presence of the first electrolyte solution for a first time period to produce a thinned intermediate material. The thinned intermediate material is combined with a second electrolyte solution that includes a strong oxidizer and at least one of a metal hydroxide salt, a weak oxidizer, and a surfactant. The thinned intermediate material is then milled in the presence of the second electrolyte solution for a second time period to produce functionalized graphene.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/163,247, filed May 24, 2016, entitled “LARGE SCALE PRODUCTION OFOXIDIZED GRAPHENE,” which is a continuation of International PatentApplication No. PCT/CA2015/051292, filed Dec. 8, 2015, entitled “LARGESCALE PRODUCTION OF OXIDIZED GRAPHENE,” which claims priority to and thebenefit of U.S. Provisional Patent Application No. 62/089,583, filedDec. 9, 2014, entitled “Large Scale Production of Partially OxidizedGraphene,” the disclosures of which are hereby incorporated by referencein their entirety.

BACKGROUND

Graphene is a single, one atomic layer of carbon atoms with severalexceptional electrical, mechanical, optical, and electrochemicalproperties, earning it the nickname “the wonder material.” To name justa few, it is highly transparent, extremely light and flexible yetrobust, and an excellent electrical and thermal conductor. Suchextraordinary properties render graphene and related thinned graphitematerials as promising candidates for a diverse set of applicationsranging from energy efficient airplanes to extendable electronic papers.For example, graphene based batteries may allow electric cars to drivelonger and smart phones to charge faster. Other examples includegraphene's ability to filter salt, heavy metals, and oil from water,efficiently convert solar energy, and when used as coatings, preventsteel and aluminum from rusting. In the longer term, thinned crystallinegraphite in general promises to give rise to new computational paradigmsand revolutionary medical applications, including artificial retinas andbrain electrodes.

SUMMARY

Embodiments described herein relate generally to the large scaleproduction of functionalized graphene. In some embodiments, a method forproducing functionalized graphene includes combining a crystallinegraphite with a first electrolyte solution that includes at least one ofa metal hydroxide salt, an oxidizer, and a surfactant. The crystallinegraphite is then milled in the presence of the first electrolytesolution for a first time period to produce a thinned intermediatematerial. The thinned intermediate material is combined with a secondelectrolyte solution that includes a strong oxidizer and at least one ofa metal hydroxide salt, a weak oxidizer, and a surfactant. The thinnedintermediate material is then milled in the presence of the secondelectrolyte solution for a second time period to produce functionalizedgraphene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowchart illustrating a method of producingfunctionalized graphene, according to an embodiment.

FIGS. 2A and 2B show example schematics of the process of milling in avessel containing graphite, grinding media and an electrolyte solution,according to an embodiment.

FIGS. 3A-3F are a series of SEM micrographs of a wide variety offew-layer graphene, according to an embodiment.

FIGS. 4A and 4B are plots of the lateral size distribution ofgraphene-based particles that comprise few-layer graphene samples,according to an embodiment.

FIG. 5 is a plot of Raman spectra for a series of different few-layergraphene sheets, and bulk graphite, according to an embodiment.

FIGS. 6A-6G are plots showing the two peak deconvolution of the Ramanspectra of different few-layer graphene sheets and bulk graphiteindicating the presence of a plurality of graphene layers, according toan embodiment.

FIGS. 7A and 7B are plots showing the shift of the 2D band peak as afunction of the thickness of few-layer graphene samples, according to anembodiment.

FIG. 8 is alternative plot providing a compact view of the number oflayers in few-layer graphene samples, according to an embodiment.

FIG. 9 is a plot showing simulated results of the number of layers infew-layer graphene samples, according to an embodiment.

FIGS. 10A-10F are examplary plots of X-ray photon spectroscopy (XPS)spectra for a series of different few-layer graphene sheets and bulkgraphite, according to an embodiment.

FIG. 11 is an example plot of example Fourier transform infraredspectroscopy by attenuated total reflection (ATR-FTIR) spectra for aseries of different few-layer graphene and bulk graphite, according toan embodiment.

FIGS. 12A-D are plots showing the results of thermo gravimetric analysisof different few-layer graphene, and bulk graphite indicating thethermal stability of these graphene-based materials.

FIGS. 13A-D are example plots of XPS, Raman, thermo gravimetric analysis(TGA), and FTIR spectra of electrostatically charged and hydroxylatedgraphene, respectively, according to an embodiment.

FIGS. 14A-14C are example plots of XPS, TGA, and FTIR spectra of atleast partially oxidized graphene, respectively, according to anembodiment.

FIG. 15 shows an example plot of thermal conductivity ofgraphene/polylactic acid (PLA) as a function of graphene concentrationby weight, according to an embodiment.

FIG. 16 shows an example experimental demonstration of the effect ofadding about 0.5 wt % of grade D graphene into UHMWPE (Ultra HighMolecular Weight Polyethylene), according to an embodiment.

DETAILED DESCRIPTION

Embodiments described herein relate generally to large scale synthesisof charged and functionalized graphene sheets, and in particular, atleast partially oxidized graphene sheets via a two-step thinning andoxidation process of precursor crystalline graphite. Graphene sheets arevery attractive for use as additives in products such as, but notlimited to, lubricants, paints, composites, special aqueous fluidsincluding drilling fluids and thermal transfer liquids, and/or the like.In some embodiments, the oxidation processes disclosed herein canincrease the mixability and/or dispersibility of graphene in suchproducts, and in solvents (e.g., polar, non-polar, etc.) in general.

In general, defects that occur in graphene and thinned graphite tend toconcentrate at the edges of the graphitic materials, leaving the surfacewith relatively low or no concentration of defects. In such embodiments,selective functionalization of the graphene edges leads to thepreservation of the desirable properties of graphene surfaces (which maybe defect-free, in some cases) while using the defected edges ofgraphene to enhance the mixability and/or dispersibility of graphene. Asedges of graphene flakes are less conductive than the low or no-defectsurfaces of the flakes, electrostatic charges produced during themilling processes of the disclosed embodiments tend to accumulate moreon the edges than on the surfaces, leading to the selectivefunctionalization of graphene (e.g., resulting in electrostaticallycharged and hydroxylated graphene sheets) if favorable chemicalconditions are met. In some embodiments, the oxidation chemistry of theelectrolyte comprising the graphene flakes or sheets can be tuned toconvert the hydroxyl ions at the edges to a mixture of hydroxyls andcarbonyls, which can enhances the mixability and/or dispersibility ofthe functionalized graphene flakes or sheets in polar as well asnon-polar solvents.

In some embodiments, the processes of the present disclosure include atwo-step milling process wherein highly charged (electrostatically),hydroxylated and oxidized thinned graphitic materials are producedstarting with a precursor crystalline graphite material. As used herein,the term “thinned graphite” refers to crystalline graphite that has hadits thickness reduced to a thickness from about a single layer ofgraphene to about 1,200 layers, which is roughly equivalent to about 400nm. As such, single layer graphene sheets, few-layer graphene (FLG)sheets, and in general multi-layer graphene sheets with a number oflayers about equal to or less than 1,200 graphene layers can be referredas thinned graphite. As used herein, the term “few-layer graphene” (FLG)refers to crystalline graphite that has a thickness from about 1graphene layer to about 10 graphene layers.

In some embodiments, the disclosed processes for thinning precursorcrystalline graphite may also reduce the lateral size of the precursorcrystalline graphite. In other words, as layers of graphene sheets areremoved from crystalline graphite, the in-plane sizes of the resultingthinned product may also be reduced. In such embodiments, the quality ofthe thinned product and/or the efficiency of the thinning process may berepresented by a parameter such as an aspect ratio that incorporatesinformation on the thickness and the lateral size of the thinnedgraphitic material. For example, one may define the aspect ratio as theratio of lateral size or in-plane dimension to thickness. Note thatother definitions for an aspect ratio are possible and may be adoptedbased on the circumstances of the situation (e.g., based on geometry ofthe product, etc.). In general, the aspect ratio provides information onthe “efficiency” and/or effectiveness of producing thinned graphitewhile avoiding or minimizing reduction in lateral sheet size. Forexample, if a thinned crystalline graphite product has an averagelateral dimension of 300 μm and a thickness of 200 nm, the aspect ratioas defined above becomes 300,000/200 (i.e., 1,500). However, a processthat reduces the thickness of the same precursor graphite to 100 nmwhile attaining average lateral dimension of 100 μm (i.e., aspect ratioof 1,000) may be deemed as less efficient, and the end result may beconsidered as lower quality in comparison to the previous example (evenwith a thinner end result) since the lateral size is reducedcomparatively on a larger scale.

In some embodiments, the precursor and/or the resulting thinned graphitemay not have a regular shape that allows for a convenient identificationof a measure of a lateral size, or even a thickness. For example, asdescribed herein, the precursor graphite can assume different forms,including rods, fibers, powders, flakes, and/or the like. However, insome embodiments, depending on at least the geometry of the precursorgraphite/thinned graphite, generalized definitions of thickness and/orlateral size can be used in characterizing these quantities. In someembodiments, the thickness and/or the in-plane lateral size ofcrystalline graphite in irregular forms can be characterized by asuitable linear dimension, and/or average of linear dimensions. Forexample, the thickness can be defined as some suitable length (e.g.,height from topmost layer to bottom-most layer of a regularly layeredgraphite flake, average height if irregularly shaped, etc.) insubstantially the same direction as the direction normal to the surfacesof the layered graphene sheets. As another example, the lateral size ofcrystalline graphite may be defined by some appropriate linear dimensionand/or combination of dimensions along the surface of the graphite(e.g., radius, diameter, average of several linear dimensions along thesurface, a linear dimension appropriately normalized by shape factorsthat take the geometrical irregularity of the graphite intoconsideration, etc.). In any case, suitable linear dimensions thatcharacterize the thickness and the lateral size of crystalline graphitein a reasonable manner may be used in defining the aspect ratio as theratio of the lateral size to the thickness. For example, if the in-planeshape of the material can not be modeled by regular geometrical objectsrelatively accurately, the linear dimension can be expressed bycharacteristic parameters as is known in the art (e.g., by using shapeor form factors).

In some embodiments, the processes disclosed herein for thinningprecursor graphitic materials can produce thinned graphite (e.g., singlelayer, bilayer, few-layer and multi-layer graphene, etc.) of variedthicknesses and lateral sizes. For example, the disclosed thinningprocess can achieve thinned end products with thickness (as definedabove, for example) less than about 1,500 layers (approximately 500 nm),about 400 nm, about 300 nm, about 200 nm, about 100 nm, about 50 nm,about 30 nm, about 10 nm, etc. In some embodiments, the lateral sizes(as defined above, for example) of the thinned end products may be aslarge as about 500 μm, about 250 μm, about 100 μm, about 1000 nm, about500 nm, about 250 nm, about 100 nm, about 50 nm, about 10 nm, etc. Assuch, thinned graphitic products with a wide range of aspect ratiosranging from about 10 nm/500 nm (about 0.2) to about 500 μm/10 nm (about50,000) can be obtained from the thinning processes disclosed in theinstant application.

In some embodiments, as indicated above, the aforementioned two-stepmilling process brings about not only the thinning of precursor graphiteinto single, few-layer and/or multi-layer graphene sheets, but also thecharging and functionalization of the thinned graphitic material. Aswill be described below in more details, the thinning and/orfunctionalization of graphite can be facilitated by oxidizers that mayplay varied roles based on their oxidation potential. For example,during the first step of the two-step thinning process, a “weak”oxidizer may be used to facilitate the shearing of sheets of graphenefrom the precursor graphite. In some embodiments, this can beaccomplished when the oxidizer interacts with electrostatic charges inthe electrolyte solution comprising the oxidizer and causes the releaseof atomic oxygen, which then intercalates the layered crystallinegraphite and weakens the bonds between the layers. In some embodiments,a “weak” oxidizer refers to a chemical agent with an oxidation potentialless than about 1.5V, about 1.25V, about 1.0V, about 0.75V, about 0.5V,about 0.25V, about 0V, about −1V, about −2V, about −3V, etc.

In some embodiments, during the second step of the two-step millingprocess, a “strong” oxidizer may be used to facilitate the conversion ofhydroxyls bonded to the edges of a hydroxylated graphitic material intocarbonyl groups. In other words, the strong oxidizer leads to the atleast partial oxidization of graphene sheets where hydrogen atoms fromthe hydroxyls at the hydroxylated edges are released, leaving behindoxygen doubly bonded to a carbon atom, i.e., partially oxidized graphenesheets. In most embodiments, the oxidizers capable of facilitating theconversion of hydroxyls to carbonyls have strong oxidation potentials,hence the term “strong” oxidizer. In some embodiments, a “strong”oxidizer refers to a chemical agent with an oxidation potential greaterthan about 1.5V, about 1.6V, about 1.75V, about 1.9V, about 2.25V, about2.5V, about 2.75V, about 3V, etc.

In some embodiments, methods and systems for producing electrostaticallycharged and hydroxylated graphene sheets from crystalline precursorgraphite are disclosed. In some of these embodiments, the methodsinclude a two-step process where the crystalline graphite (e.g., flakegraphite (FG) powder) can be thinned to single, few or multi-layergraphene sheets with charged edges that facilitate the hydroxylationand/or carbonyl-ation of the edges of the graphene sheets. In someembodiments, the first step of the two-step process comprises combininglarge crystalline precursor graphite with electrolyte slurry into agrinding vessel or jar such as, but not limited to, an attritor. In someembodiments, the electrolyte slurry includes at least a metal hydroxide(MH) salt and an aqueous solution comprising a polar solvent (e.g.,water, ethanol, 1-propanol), a weak oxidizer and a surfactant. Thegrinding vessel and/or the associated grinding media may be chosen basedon the amount of electrostatic charge one desires to generate during thedisclosed processes; as such, a selection of the grinding vessel and/orthe associated grinding media can be used as a control over the charginglevel of the thinned graphene sheets. For example, vessels or jars madefrom insulating material such as Alumina or Zirconia accompanied withsame/similar type of grinding balls generate higher electrostaticcharges than stainless steel jars and balls. Another parameter that canbe used to control the generation and amount of the electrostatic chargeto be produced during the disclosed milling processes is the rotationspeed. For example, medium rotation speed of the grinding vessel canintroduce electrostatic charges on and within the electrolyte, resultingin the ionization of the MH salt.

In some embodiments, the hydroxide ions released into the electrolyteslurry from the MH salt can diffuse into the interlayer spacing of thelayered crystalline precursor graphite, i.e., the hydroxide ionsintercalate graphite so as to cause the formation of n-stageintercalated graphite. In such embodiments, n can be any one of naturalnumbers less than the number of graphene layers in the crystallineprecursor graphite. For example, n can be 1, 2, 3, 4, 5, etc. In someembodiments, the n-stage intercalated graphite can be a combination ofdifferent stage intercalated graphite. For example, the hydroxide ionscan intercalate graphite so as to cause the formation of 1-stage and2-stage intercalated graphite, and/or the like. In some embodiments,this may facilitate the exfoliation of layers of graphene sheets fromthe precursor graphite by the shearing forces induced during therotation of the grinding vessel or jar. In some embodiments, theresulting graphene sheets tend to maintain the initial lateral size ofprecursor graphite while their thickness may be dramatically lowered, inparticular in comparison to the thickness of the initial precursorgraphite. In some embodiments, the resulting graphene product (which mayinclude thinned graphitic materials such as, but not limited to, single,few and multi-layer graphene sheets, etc.) may be post-processed (e.g.,filtered, washed, dried, and/or the like) so as to at least removeextraneous by-products. In some embodiments, at the end of the firststage of the two-step milling process, the resulting graphene productmay appear to be black, and may exhibit a fluffy structure. Further, theresulting product may be electrostatically highly charged and containhydroxyl molecules, and the electrostatic charges and the hydroxylmolecules may appear more at the edges of the resulting graphene sheetsthan on the surface (e.g., towards the center).

In some embodiments, in the second stage of the two-step millingprocess, the graphitic product from the first step (e.g., dried graphenesheets) may be combined with a slurry that includes at least an MH salt,a strong oxidizer, and an aqueous solution including a polar solvent(e.g., water), a non-polar solvent (e.g., acetonitrile), a weak oxidizerand a surfactant. This combination may be effected in several ways. Forexample, the resulting graphene products may be transferred into asecond grinding vessel containing at least some of the ingredients ofthe second step of the two-step process (e.g., strong oxidizer,non-polar solvent, weak oxidizer, etc.). In some embodiments,ingredients that are particularly used during the second step such as,but not limited to, the strong oxidizer, the non-polar solvent, etc.,may be added into the grinding vessel of the first step of the two-stepprocesses. In any case, in some embodiments, the combination comprisingthe graphene products of the first step process, a strong oxidizer, aweak oxidizer, a polar solvent, a non-polar solvent, an MH salt and asurfactant may be rotated in a grinding vessel (e.g., attritor) for aperiod of time at a desired rotation speed. In some embodiments, theresulting hydroxylated product may appear to be brown and exhibit afluffy structure. In some embodiments, the resulting product may bepost-processed (e.g., filtered, washed, dried, and/or the like). In someembodiments, the resulting product can be at least partially oxidizedthinned graphene sheets with hydroxylated edges where at least part ofthe hydroxyls bonded to the edges of the graphene sheets are convertedinto carbonyl molecules. As the carbonyl molecules tend to be moreactive for bonding than the hydroxyl groups, in some embodiments, theresulting at least partially oxidized graphene sheets represent anenhanced dispersibility and/or mixability in different kinds ofsolutions including polar and non-polar solvents.

In some embodiments, the first step of the two-step process comprisesthe thinning precursor crystalline graphite in the presence of anelectrolyte solution. As used herein, the term “crystalline graphite” or“precursor crystalline graphite” refers to graphite based material of acrystalline structure with a size configured to allow milling in agrinding or milling vessel or jar. For example, the crystalline graphitecan be layered graphene sheets with or without defects, such defectscomprising vacancies, interstitials, line defects, etc. The crystallinegraphite may come in diverse forms, such as but not limited to orderedgraphite including natural crystalline graphite, pyrolytic graphite(e.g., highly ordered pyrolytic graphite (HOPG)), synthetic graphite,graphite fiber, graphite rods, graphite minerals, graphite powder, flakegraphite, any graphitic material modified physically and/or chemicallyto be crystalline, and/or the like. In some embodiments, the crystallinegraphite can be graphite oxide. The lateral or in-plane size as well asthe thickness of the ordered graphite can assume a wide range of values.For example, using an appropriate measure to quantify the lateral sizeof the ordered graphite as discussed above (e.g., mean lateral sizes,diameter, etc., depending on the shape, for example), the lateral sheetsize of the ordered graphite can range from about 10 nm to about 500 μm.The thickness of the graphite can be as large as desired as long as itssize may not interfere with the milling or thinning processes.

In some embodiments, the electrolyte solution in which the two-stepmilling process takes place comprises polar solvents. An example of apolar solvent may be purified water such as, but not limited to, doubledistilled deionized water. Other examples include propanol, butanol,acetic acid, ethanol, methanol, formic acid, and/or the like. In someembodiments, some of these solvents may also be used for other purposesduring the milling process. For example, ethanol may be used as ade-foaming agent.

In some embodiments, during the two-step milling process, a weakoxidizer may be used to interact with hydroxyl ions to generate atomicoxygen that can intercalate graphite and weaken the interlayer van derWaals bonds. Owing to its conductive characteristics, the weak oxidizercan be used as a dissipating agent for the electrostatic chargesproduced during the milling process. That is, the weak oxidizer may beconfigured to assist with the dissipation of the electrostatic chargesthroughout the electrolyte solution. As used herein, a “weak” oxidizerrefers to a chemical agent with an oxidation potential less than about1.5V. Examples of a weak oxidizer include diluted hydrogen peroxide,chromate, chlorate, perchlorate, and/or the like. In this context, adiluted oxidizer may mean an oxidizer that contains about 30% by weightof the oxidizing agent. For example, a diluted weak hydrogen peroxideoxidizer has about 30% by weight of the oxidizing agent hydrogenperoxide. In some embodiments, the diluted oxidizer may contain fromabout 10% to about 50%, from about 15% to about 45%, from about 20% toabout 40%, from about 25% to about 35%, and/or the like of the oxidizingagent by weight. In some embodiments, the discussion above with respectto MH salt applies to both steps of the disclosed two-step process.

In some embodiments, a metal hydroxide (MH) salt configured to interactwith electrostatic charges to produce metal and hydroxide ions can beadded into the grinding vessel or jar of the two-step process disclosedherein. As discussed above, the hydroxyl ions may further interact withelectrostatic charges to generate atomic oxygen that can intercalatecrystalline graphite and weaken the interlayer van der Waals bonds so asto facilitate the shearing of the graphene sheets of the graphite. Insome embodiments, the hydroxide ions can also diffuse into theinterlayer spacing of the layered crystalline precursor graphite tointercalate graphite and facilitate the exfoliation of graphene sheetsby the shearing forces generated during the rotation of the grindingvessel or jar. In some embodiments, the metal hydroxide salt can beformed from a combination of a hydroxyl ion and a metal selected fromalkali metals, alkaline earth metals, boron group elements, etc.Examples of metal hydroxide salts that can be used for the disclosedtwo-step processes include hydroxides of Li, Na, K, Cs, Be, Mg, Ca, Sr,Ba, B, Al, Ga, In, Cs, Rb, Ti, mixtures thereof, and/or the like. Insome embodiments, the amount of metal hydroxide salt to be used in thedisclosed processes can assume a wide range of values. For example, insome embodiments, the amount of metal hydroxide salt may range fromabout 1% to about 30% by weight about X% to about Y% by volume of theelectrolyte solutions of the two step process. In some embodiments, theamount may range from about 5% to about 25%, from about 10% to about20%, from about 14% to about 16% by weight, etc. In some embodiments,the amount may be any amount equal to or less than the maximum amountthat is soluble in the electrolyte solution. In some embodiments, inparticular for the purpose of doping resulting graphene sheets withmetal particles, the amount of metal hydroxide salt can be increased toabout 90% of the solution by volume.

In some embodiments, the type of MH salt that may be used in thetwo-step process may depend on the desired production yield of theprocess to reduce the precursor crystalline graphite into thinned andcharged graphene sheets. In some embodiments, production yield may bedefined as the proportion of precursor graphitic material that has beenreduced to thinned graphite of a defined number of graphene sheets orless. In some embodiments, the production yield of the two step processmay vary based on the type of metal that is part of the MH salt. Forexample, in some embodiments, for a high production yield of greaterthan about 60% (i.e., greater than about 60% of the precursor graphiteby weight is converted into thinned graphene of about 10 layers as aresult of the process), the metal that is part of the MH salt may be amember of the alkali and/or alkaline earth metals, comprising Li, Na, K,Cs, Be, Mg, Ca, Sr and Ba. In some embodiments, for a low productionyield of less than about 60%, the metal may be a member of the borongroup elements, comprising B, AI, Ga, In, and Ti. In some embodiments,the MH salt used in the milling or grinding processes disclosed hereinmay be a single MH salt comprising a metal and a hydroxide ion, and insome embodiments, the MH salt may be a mixture of any of theabove-identified metal hydroxide salts. In some embodiments, thediscussion above with respect to MH salt applies to both steps of thedisclosed two-step process.

In some embodiments, surfactants can be included in the two-step processso as to avoid or minimize clamping of the end products of the process.Further, surfactants may increase the conductivity of the mixture in thegrinding vessel, allowing for an increased diffusion of the hydroxylions and thereby contributing to the exfoliation of graphene layers fromthe crystalline graphite as discussed above. In addition, surfactantsmay be used to facilitate the mixing of polar and non-polar solventsthat in general are adverse to mixing. Further, surfactants may also beused to facilitate contact between an ingredient that is adverse tomixing with a given solvent and the solvent. For example, surfactantsmay be used to facilitate contact between hydrophobic graphite materialsand water. Examples of surfactants that can be used for such purposeduring two-step process comprise sodium dodecyl sulfate (SDS), sodiumdodecyl benzene sulfonate, pyridinium (PY+), thionin acetate salt,triton, mixtures thereof, and/or the like.

In some embodiments, the concentration of surfactants to be used duringthe milling processes can be determined based on the desire to maintainbalance between the thinning of the crystalline graphite and thereduction in its lateral size. As discussed above, in some embodiments,surfactants enhance the shearing force on crystalline graphite andfacilitate the thinning of the crystalline graphite. On the other hand,a large amount of surfactants (e.g., more than the amount used to avoidor minimize agglomeration of crystalline graphite) can lead to reductionin lateral size, which may be undesirable in some circumstances.Accordingly, in some embodiments, an average concentration of betweenabout 1 μMolar and about 200 μMolar of surfactants can be consideredsufficient during the thinning and charging processes of precursorgraphite. In some embodiments, the average concentration may range fromabout 5 μMolar to about 150 μMolar, from about 10 μMolar to about 100μMolar, from about 10 μMolar to about 50 μMolar, from about 50 μMolar toabout 100 μMolar, and/or the like. In some embodiments, the discussionabove with respect to surfactants applies to both steps of the disclosedtwo-step processes.

In some embodiments, the electrolyte solution used for the two-stepmilling process can have a very conductive and alkaline environment. Forexample, the pH level may range from almost neutral to very strongbasic. In some embodiments, the pH level may range from about 8 to about14, from about 9 to about 14, from about 9 to about 11, from about 12 toabout 14, and/or the like. The alkalinity may follow as a result of thesmall ionization potential of MET salt upon dissolving in the solvent(s)of the electrolyte solution.

In some embodiments, the disclosed two-step grinding or millingprocesses can be carried out in any type of grinding or milling systemthat comprises a vessel and allows for the shearing, exfoliation,charging, hydroxylation, etc., of the crystalline precursor graphite.Examples of such a system that can be used for the two-step processinclude milling vessels such as but not limited to ball mills, rodmills, pebble mills, autogenous mills, semi-autogenous mills, rollermills (e.g., jar roller mills, ring mills, frictional-ball mills, etc.),attritors, planetary mills, jet mills, aerodynamic mills, shear mixers,and/or the like. In some embodiments, the mill jars or vessels can bemade from conductive materials, insulators and/or semi-conductors,including ceramic materials, alumina, stainless steel, and/or zirconia,and can also be lined with materials such as polyurethane, rubber, etc.In some embodiments, the vessels may include grinding media for aidingin the grinding/shearing of precursor materials such as graphite. Insome embodiments, the grinding media can be made from the same type ofmaterials as the vessel or jar in which the grinding media are beingused. As such, for example, the vessels and/or the grinding media may beelectrically conductive, and comprise materials such as stainless steel,metals and/or alloys (e.g., tungsten carbide). In some embodiments, thevessels and/or the grinding media may be coated with electricallyconductive material. In general, the vessels and/or the grinding mediamay be configured to conduct electric charges. For example, the grindingmedia can be made from alumina, zirconia, stainless steel, etc. In someembodiments, the grinding media may assume different forms. For example,the grinding media can be at least substantially a ball (hence thecommon term “ball milling”), at least substantially a cylinder, at leastsubstantially a rod, and in fact any shape capable of aiding in thegrinding/shearing of precursor materials. As used herein, the term“grinding media” or “milling balls” refer to any grinder that can beused in the exfoliation and thinning of crystalline graphite in ballmilling jars. Even though the common nomenclature “milling balls” isused, the grinding media or the milling balls are not limited to aparticular geometry, and can have any desired property such as shape,size, composition, etc.

In some embodiments, with reference to FIG. 1, crystalline graphite, asolvent (e.g., polar), grinding media, a MH salt, a weak oxidizer and asurfactant can be added into a milling vessel to commence the first stepof the two-step milling process, e.g., step 101. For example, largeflake size graphite powder, water, hydrogen peroxide, a metal hydroxidesalt such as potassium hydroxide (KOH), and a surfactant such as SDS maybe added into a milling vessel. In some embodiments, electrolytemixtures such as the one in the preceding example may be placed into amilling vessel or jar made from electrically conductive materials suchas stainless steel, metal or alloys, and milled or rotated for a periodof time and at a speed of rotation configured to generate electrostaticcharges in the electrolyte mixture, e.g., step 102. In some embodiments,the speed of the rotation may be configured to reduce the initialthickness of the graphite without substantially affecting its lateralsize. For example, the stronger mechanical interaction between thegrinding media and the crystalline graphite that could result as aresult of higher milling vessel rotational speed can reduce not only thethickness of the crystalline graphite, but also its lateral size.Accordingly, during the first step of the two-step milling process, themilling speed can range from about 10 rotations per minute (rpm) toabout 500 rpm. In some embodiments, the milling speed can range fromabout 10 rpm to about 300 rpm, from about 10 rpm to about 250 rpm, fromabout 10 rpm to about 150 rpm, from about 10 rpm to about 100 rpm, fromabout 50 rpm to about 300 rpm, from about 150 rpm to about 250 rpm, fromabout 200 rpm to about 250 rpm, and/or the like.

In some embodiments, the number and/or sizes of grinding media in themilling vessel or jar can depend on milling process related factors suchas but not limited to the running time, the rotational speed,amount/size of the crystalline graphite, average size of the grindingmedia, and/or the like. For example, for a given amount of crystallinegraphite, there can be some milling ball sizes (conversely number ofmilling balls) that can be particularly beneficial in effecting a moreefficient shearing of crystalline graphite layers depending on the speedand the length of the ball milling process. In some embodiments, thegrinding media may be small sized balls and their amount may be chosenbased on the amount of crystalline graphite to be treated. For example,the amount of the grinding media may be chosen so that during themilling process, the weight proportion of grinding media to crystallinegraphite may be in the range of from about 5:1 to about 20:1. In someembodiments, the proportion may be in the range of from about 7:1 toabout 15:1, from about 9:1 to about 12:1, about 10:1, and/or the like.In such embodiments, the average size of the grinding media (e.g.,balls) may be in the range of from about 3 mm to about 20 mm, from about5 mm to about 15 mm, from about 8 mm to about 12 mm, and/or the like.

In some embodiments, the duration of the first step milling process toreduce the thickness of the precursor graphite and arrive athydroxylated thinned graphite or graphene sheets may range from aboutfrom about 2 hours to about 24 hours. In some embodiments, the durationmay range from about 2 hours to about 12 hours, from about 2 hours toabout 6 hours, from about 2 hours to about 4 hours, and/or the like.

In some embodiments, the rotation during the two-step process maygenerate a shearing force by the grinding media that may be configuredto provide enough energy to the electrostatic charges in the electrolytesolution to react with the salts (which may be polarized) in thesolution. In some embodiments, the reaction between the electrostaticcharges and the MH salt may generate atomic oxygen. An additionalmechanism for the generation of atomic oxygen in the electrolyte mixturecan be through the interaction of the weak oxidizer with the hydroxylions that may be present in the mixture (from the MH salt, for example).In such embodiments, the weak oxidizer may interact with the hydroxylions to release atomic oxygen that may also be used for the exfoliationof the graphite. For example, in some embodiments, the generated and/orreleased atomic oxygen may diffuse in between layers of the crystallinegraphite and increase the in-plane separation. When the in-planedistance passes beyond a certain distance, in some embodiments,inter-planar bonds (covalent, van der Waals, etc.) of graphite maybecome weak enough that a gentle shearing force may exfoliate the layersfrom the crystalline graphite. In some embodiments, hydroxyl anions inthe electrolyte may also diffuse in between layers of graphite andweaken the inter-layer bonding. In some embodiments, the solvent mayalso penetrate between layers of the ordered graphite and weaken theforces that hold the layers together, thereby contributing to thethinning of the crystalline graphite during the milling process.

In some embodiments, the first step milling process may be interruptedevery so often to allow the escape of gas for various reasons (e.g.,safety). For example, in some embodiments, the milling process may bestopped every 30 minutes to evacuate gas by-products that are producedduring the rotation/milling of the milling vessel. In some embodiments,the process of milling may also be performed in a manner designed toavoid evaporation of solvents such as water from the aqueous electrolytesolution. For example, milling vessels or jars used in the millingprocesses may be kept at a temperature formulated to avoid evaporationof the solvents, an example being room temperature.

In some embodiments, the resulting product of the first milling step mayappear black and possess a fluffy structure. This resulting product maybe post-processed to at least remove extraneous by-products or residuessuch as, but not limited to, metallic ions, surfactants, metal salts,etc. For example, the product may be removed from the milling vessel orjar and washed with one or more of water, hydrochloric acid (HCl),ethanol, and/or the like, e.g., step 103 of FIG. 1. In some embodiments,the washing may be followed by vacuum filtration and vacuum drying. Theresulting product can be single or thinned few layer graphene (FLG)sheets that are highly charged and hydroxylated mainly at the edges, insome embodiments.

In some embodiments, the graphene sheets from the first step of thetwo-step milling process may include graphene or thinned graphitematerials with lateral sizes that are comparable to the precursorgraphite but with thickness of few graphene layers, including singlelayer graphene sheet. For example, the lateral sheet size of thegraphene sheets may be about 500 μm while the number of layers may bebetween about 10 and about 100 graphene layers, less than about 10graphene layers, less than about 3 graphene layers, and a singlegraphene sheet. In some embodiments, the graphene sheets may be highlyelectrostatically charged and may contain hydroxyl molecules that residemostly on the edges rather than towards the center of the surfaces ofthe graphene sheets. As such, this may lead to the selectivefunctionalization of the edges in comparison to the entire surfaces ofthe thinned graphene sheets.

At least some embodiments of the first step of the disclosed two-stepmilling process have been employed experimentally to reduce thethickness of precursor crystalline graphite and produce highlyelectrostatically charged, hydroxylated graphene sheets. In someembodiments of the experimental results, at least some of these graphenesheets can be conveniently classified into the following classes orgrades:

-   -   Grade A: A few-layer graphene powder of about 3 to 4 graphene        layers and lateral size (e.g., flake diameter) of about 5 μm to        20 μm. These graphene sheets have been found to exhibit highly        activated edges and low defect density.    -   Grade B: A few-layer graphene powder of about 2 to 3 graphene        layers and lateral size (e.g., flake diameter) of about 0.5 μm        to 5 μm. These graphene sheets have been found to exhibit highly        activated edges and low defects.    -   Grade C: A few-layer graphene powder with similar properties as        Grade A, but with moderately activated edges.    -   Grade D: A few-layer graphene powder with similar properties as        Grade B, but with moderately activated edges.

In some embodiments, the lateral sizes and the thicknesses of thesevarious grades may be obtained from any number of experimentaltechniques. For example, FIGS. 3A-3F show scanning electron microscopy(SEM) images of thinned graphene products that belong in Grade A (FIG.3A), Grade B (FIG. 3B), Grade C (FIG. 3C), and Grade D (FIG. 3D). Froman analysis of the SEM images, in some embodiments, grades A and C havebeen found to include particles or flakes ranging in lateral size fromabout 5μm to about 20 μm (FIG. 4A), and grades B and D include particlesranging in lateral size from about 0.5 μm to about 5μm (FIG. 4B). Insome embodiments, in addition to size information, the analysis may alsoreveal the distribution of structures of the graphene sheets from thefirst step. For example, Grade B (FIG. 3B) shows thin layered structuresstacked together.

With respect to thickness and defect density of the resulting productsof the milling process, in some embodiments, Raman spectroscopy can beused to characterize these properties. In some embodiments, visiblelight (e.g., 532 nm wavelength light corresponding to 2.33 eV energy)may be used to obtain Raman spectra for bulk crystalline graphite, GradeA few layer graphene (FLG) 502, Grade B FLG 503, Grade C FLG 504 andGrade D FLG 505, shown in FIG. 5. In FIG. 5, the Raman spectra for allthe grades show peaks that are the result of in-plane vibrational modescaused by excitations due to the laser used for the spectroscopy. Thesepeaks or bands include the primary in-plane mode of the so-called G bandaround wavenumber 1580 cm⁻¹, a different in-plane vibration mode of theso-called D band around wavenumber 1300 cm⁻¹, and a second-orderovertone of the D band, the so-called 2D band around wavenumber 2700cm⁻¹. Analysis of the D peaks as discussed in Phys. Rev. Lett., 97,187401 (2006) and Journal of Physics: Conference Series 109 (2008)012008, the entire contents of both of which are incorporated herein byreference in its entireties, can provide information on the thicknessesof the graphene sheets of the different grades resulting from thedisclosed milling processes. In some embodiments, one may also use thetechniques disclosed in J. Raman Spectrosc. 2009, 40, 1791-1796, theentire contents of which is incorporated herein by reference in itsentirety, to analyze the G peaks and evaluate the number of layers inthe graphene sheets. Further, in some embodiments, an analysis of the Dpeaks and the G band with respect to each other may reveal informationon defect density of the graphene sheets. For example, the ratio of theintensity at the G band to the intensity at the D band may serve as aparameter for characterizing defect density. For example, a large ratiomay indicate the presence of little or no defects in the resultinggraphene products while a small value of the ratio indicates largedefect presence. From the results of the Raman spectroscopy (FIG. 5),the average value of the ratio for the graphene sheets of Grades A, B,C, and D can be calculated to be about 20, a large value indicating lownumbers of defects in the resulting graphene sheets of the first step ofthe two-step process (and further indicating that the graphene sheetshave large sizes).

With respect to the analysis of the D peaks, in some embodiments,changes in shape, width, and position of the 2D peaks of the Ramanspectra may be used to identify the thicknesses of the grades ofgraphene sheets being investigated. Using the techniques discussed inthe above noted Journal of Physics article (Journal of Physics:Conference Series 109 (2008) 012008), a two peaks deconvolution usingLorentzian functions can be chosen, as shown in FIGS. 6A-6G, indicatingthat the number of layers exceeded two. In some embodiments, ananalytical comparison of the 2D peaks amongst the different gradegraphene sheets may reveal that the 2D peak shifts from a higherwavenumber for crystalline graphite with large number of graphene sheetsto a lower wavenumber for few-layer graphene such as the thinnedproducts of Grade D, as shown in FIGS. 7A-B. In some embodiments, onemay compare the 2D peak positions for the different grades with the dataprovided in Chem. Comm., 2011, 47, 9408-9410, the entire contents ofwhich is incorporated herein by reference in its entirety, to establishthe number of layers in the graphene sheets of Grades A-D and bulkcrystalline graphite. FIG. 8 provides a compact view of the number oflayers of the graphene sheets of Grades A-D and bulk crystallinegraphite in relation to the 2D peak positions. A tabulation of the 2Dpeaks and the number of layers for each grade is given in the tablebelow:

2D_(A) peak 2D_(B) peak Number of Sample position position layersGraphite 2682.03 cm⁻¹ 2716.67 cm⁻¹ >=10 Grade A 2665.26 cm⁻¹ 2700.34cm⁻¹ 2 to 3 Grade B 2666.09 cm⁻¹ 2703.01 cm⁻¹ 4 to 5 Grade C 2666.28cm⁻¹ 2702.82 cm⁻¹ 2 to 3 Grade D 2666.37 cm⁻¹ 2699.72 cm⁻¹ 4 to 5

With respect to the analysis of the G peak, in some embodiments, one mayemploy the disclosure of the noted J. Raman Spectroscopy article (J.Raman Spectrosc. 2009, 40, 1791-1796) to perform an empirical evaluationof the number of lavers can also be determined from G peak positionusing the equation

$N = {N_{Graphite} - \frac{K}{1 + n^{1.6}}}$

where N is the wavenumber of the G peak of the FLG n is the number oflayers, N_(Graphite) is the wavenumber of bulk graphite corresponding tolarge value of n (e.g., n>10), and K a calculated coefficient. Forexample, using the wavenumber for the aforementioned G peaks of GradeA-D, and setting the wavenumber of bulk graphite N_(Graphite) to beabout 1579.38 cm⁻¹, the coefficient K can be calculated to be about54±3. In some embodiments, this method of evaluation gives someconsistent results for grades B and D with about 2 to 3 layers; however,in some embodiments, a small difference can be observed for Grades A andB indicating up to 4 layers (e.g., instead of 3). FIG. 9 providescalculated values for the number of layers of the graphene sheets ofGrades A-D and bulk crystalline graphite in relation to the G peakpositions. From a synthesis of the above two methods (analysis of the Dpeaks and the G peaks) of determining the number of layers in samples ofGrades A-D, in some embodiments, a reasonable determination of about 2-3layers for Grades B and D and about 3-4 for Grades A and C can be made.

As mentioned above, in some embodiments, graphene sheets that are theresult of the first step of the disclosed two-step process are highlycharged and contain edges that are hydoxylated, i.e., hydroxyl groups(OH⁻) are bonded to the edges of the graphene sheets. The appearance ofhydroxyl groups at the edges serve as chemical “hooks” for the graphenesheets, and an experimental technique such as X-ray Photon Spectroscopy(XPS) may be used to identify the hydroxyl groups and characterize thesurfaces also. For example, for the graphene sheets of grades A, B, Cand D, FIGS. 10A-10F show the XPS spectra of Grade A (FIG. 10A), Grade B(FIG. 10B), Grade C (FIG. 10C) and Grade D (FIG. 10D) with some of thepeaks corresponding to the atomic orbitals identified. In someembodiments, deconvolution can be performed to semi-quantify the carbonspecies on the surface where the same pattern was used for all fivegrades. In some embodiments, four intensity peaks may be identified:

-   -   Peak from carbon sp² due to graphitic carbon. In some        embodiments, this peak may be the most intense because graphene        is composed of a vast majority of carbon atoms in sp².    -   Peak from carbon sp³ due to tetrahedral bonded carbon. This        carbon species can be found on the edges of the graphene        platelets.    -   Peak from carbon-oxygen (C—O) is due to the hydroxyl groups on        the edges of graphene platelets. This shows that the milling        process is capable of effectively functionalizing graphene        platelets edges.    -   Peaks from π-π are typical of graphitic carbon and can be        attributed to resonance. The presence can be expected in        graphene because this is a graphitic material.        Integrals, i.e., summation of the intensities of each peak for        each grade are tabulated below, indicating that all grades        comprise activated edges with hydroxyl groups.

TABLE 1 C1s sp3 C1s sp2 C1s C—O C1s C═O C1s π-π * Grade A 10.19 58.8522.84 0 8.12 Grade B 9.23 61.71 18.54 0 10.51 Grade C 9.63 61.84 22.61 05.92 Grade D 10.01 61.95 21.21 0 6.84 Grade F 14.69 53.19 17.2 3.9410.98Confirmation of the presence of hydroxyl groups at the edges of thegraphene sheets may be obtained from other techniques such as Fouriertransform infrared spectroscopy by attenuated total reflection(ATR-FTIR), which may be used to characterize the edge activation andother properties of the various grades. FIG. 12 shows that all gradesexhibit the C—O stretching mode around 1060 cm⁻¹ and the C—OH stretchingmode around 1200 cm⁻¹. These modes confirm the presence of hydroxylgroups over the graphene flakes. Around 1600 cm⁻¹ the vibration ofgraphitic domains is observed for the graphene sheets of grades A-D, butnot for bulk graphite due to the high number of graphitic layers. Thisis further evidence that graphene sheets of grades A through D comprisefew-layers of graphene, unlike the bulk or large numbers for graphite.The O—H stretching mode around 3400 cm⁻¹ has been observed only on the13.2 (Grade C). This mode was also expected on all other grades. FIGS.13A-D provide additional example plots of X-ray photon spectroscopy(XPS) (FIG. 13A), Raman (FIG. 13B), TGA (FIG. 13C), and Fouriertransform infrared spectroscopy (FTIR) (FIG. 13D) spectra ofelectrostatically charged and hydroxylated graphene, according to anembodiment.

In some embodiments, the thermal stability of the graphene sheets ofgrades A-D may be investigated via a thermo gravimetric analysis (TGA)that tracks the thermal transitions of the materials as a function oftemperature, transitions such as, but not limited to, loss of solventand plasticizers in polymers, water of hydration in inorganic materials,and/or decomposition of the material. For example, a TGA analysis can beperformed for each grade by raising the temperature of a furnacecontaining the graphene sheets and measuring the sample weight. In FIG.12, the weight percentage of the sample remaining after mass loss as afunction of temperature when the temperature is raised to 930° C. at arate of 10° C./min in air is shown for the grades A and B (FIG. 12A) andGrades C and D (FIG. 12B). For grades A, B, C and D, the degradationstarts at around 690° C., in contrast to 800° C. for graphite and 600°C. for a graphene layer, indicating that these grades comprise few-layergraphene products, agreeing with the results of other measurements suchas Raman spectroscopy. In some embodiments, loss prior to degradationhas been observed (e.g., at less than 2%) and can be ascribed primarilyto residues from the washing process. The results in general show theheat resistance properties of grades A-D graphene sheets.

With reference to FIG. 1, in some embodiments, the graphene sheets ofthe first step of the two-step milling process (e.g., thinned graphenesheets of grades A, B, C and/or D) may be mixed with a strong oxidizerand a non-polar solvent for the second step of the milling process,e.g., step 104. In some embodiments, the strong oxidizer and thenon-polar solvent may be added into the same milling vessel as the oneused for producing the resulting products. In some embodiments, if thegraphene sheets may have been removed from the milling vessel forpost-processing, the processed (e.g., washed, filtered, etc.) graphenesheets may be re-introduced into the grinding or milling vessel. In someembodiments, the milling process may take place in a grinding vessel orjar that is different than the one used during the first step. Forexample, the first milling vessel may have been drained, and thegraphene sheets from the first step, a strong oxidizer, a non-polarsolvent and at least some of the ingredients of the first step such asthe polar solvent, the weak oxidizer, the metal hydroxide salt, thesurfactant and grinding media may be added into the mixture (forexample, in the manners (i.e., amounts, concentration, proportions,etc.) as described above with respect to the first step of the millingprocesses) to commence the second-step of the two-step milling process.Although termed as a “two-step” process, in some embodiments, thedisclosed milling process can be viewed as a single step process whereprecursor graphite is milled to reduced its thickness to few layers orless, and the resulting graphene product is further milled in thepresence of a strong oxidizer to cause the charging, hydroxylation andat least partial oxidation of the resulting product.

In some embodiments, the weak oxidizer may be included in the secondstep so as to continue the shearing and/or exfoliation process duringthe second step. For example, the crystalline precursor graphite mayhave been reduced to about 5 hydroxylated graphene sheets after thefirst step of the milling process, and the presence of the weak oxidizerduring the second step may assist in reducing the thickness of thethinned graphene sheets from about 5 layers to about 1-layer, 2-layer,3-layer graphene sheets, and/or the like.

In some embodiments, the strong oxidizer may be formulated to interactwith the hydroxyl ions bonded to the edges of the graphene sheets so asto convert the hydroxyl ions into a carbonyl group. As used herein, a“strong” oxidizer refers to a chemical agent with an oxidation potentialgreater than about 1.5V. Examples of a strong oxidizer include potassiumpermanganate, iron chloride, persulfate, fluorine, any combinationthereof, and/or the like. In some embodiments, the strong oxidizeraccomplishes the conversion of hydroxyl ions to carbonyls by removingthe hydrogen atom from the hydroxyl ion, resulting in the formation of adouble bond between the remaining oxygen atom and a carbon atom on thegraphene sheets. In some embodiments, the proportion of hydroxyl ions atthe edges of the graphene sheets that convert to carbonyl groups dependson the amount, concentration, type, etc., of the strong oxidizer used.For example, using potassium permanganate as a strong oxidizer, thesecond step of the two-step milling process may accomplish theconversion of about 20% of the hydroxyl at the edges of the graphenesheets to carbonyls.

In some embodiments, the non-polar solvent used during the second stepof the two-step milling process may be configured to aid in theproduction of hydroxyl ions as well as in the diffusion of the ions inthe electrolyte solution, which may facilitate the eventual bonding ofthe hydroxyl ions to the edges of the graphene sheets. For example, thenon-polar solvent may increase the conductivity of the solution, therebyenhancing the transfer of electrostatic charge through the solution soas to allow the charges to ionize the metal hydroxide salt and producemetal cations and hydroxide anions (i.e., hydroxyls). Further, a higherconcentration of non-polar solvent in the electrolyte solution mayincrease the diffusion length of hydroxyl ions in the solution,facilitating the bonding of hydroxyl ions to the edges of the graphenesheets.

In some embodiments, the non-polar solvent may also be configured to aidin the production of electrostatic charges during the rotation of themilling vessel during the second step of the two-step process. Inaddition, the non-polar solvent may enhance the exfoliation and/orshearing of sheets of graphene layers from the ordered crystallinegraphite (e.g., besides the solvent's role in the production ofelectrostatic charges which, as discussed above with respect to thefirst step of the milling process, contributes to the production ofatomic oxygen that exfoliates crystalline graphite). For example, thenon-polar solvent may intercalate crystalline graphite and weaken thebonds (e.g., van der Waals bonds) that keep the layers of graphiticmaterials bound in layers.

Examples of non-polar solvents comprise organic solvents, includingorganic molecules and ions. For example, organic solvents such asToluene and N-Methyl-2-pyrrolidone can be used as non-polar solvents inthe electrolyte solution during the second stage of the two-stepprocesses. As additional examples, heptane, N,N-Dimethylformamide,acetonitrile, chlorobenzene, dimethyl sulfoxide,N-methyl-2-pyrrolidinone, and/or the like can be used as non-polarsolvents for at least any of the above purposes. In some embodiments,the amount, concentration, type, etc., of the non-polar solvent usedduring the second stage may depend on the solubility of graphiticmaterials like graphene in the different solvents. For example, thesolubility of graphene may be different in different solvents, and thesolvent providing maximum solubility to graphene may be chosen forinclusion into the electrolyte solution. Accordingly, the amount of thepolar and/or non-polar solvent included during the second stage may beproportional to teach other. For example, in some embodiments, water andethanol may be used in the proportion ranging from about 1000:1 to about10:1, from about 800:1 to about 100:1, 400:1 to about 200:1, and/or thelike, by volume.

With reference to FIG. 1, in some embodiments, the graphene sheets ofthe first step of the milling process, the strong oxidizer, thenon-polar solvent, the polar solvent, the weak oxidizer, the metalhydroxide salt and the surfactant may be rotated in a milling vessel orjar at a desired speed for a period configured to allow the conversionof the hydroxyl ions bonded to the edges of the graphene sheets, e.g.,step 105. For example, the highly charged and hydroxylated graphenesheets may be milled for about 2 to 10 hours until a brown, fluffypowder is produced. In some embodiments, the milling period may rangefrom about 2 hour to about 8 hours, from about 2 hour to about 6 hours,from about 2 hour to about 4 hours, and/or the like. The rotation speedmay be medium, in the range of from about 100 rpm to about 500 rpm, fromabout 200 rpm to about 400 rpm, from about 200 rpm to about 250 rpm,and/or the like. In some embodiments, the grinding media (includingtype, amount, size, proportion to graphitic material to be milled, etc.)used during this second step of the two-step milling process may besimilar to those utilized during the first step.

In some embodiments, similar to the case of the first step of themilling process, the second step may also be interrupted every so oftento allow the escape of gas that has built up during the rotation of themilling vessel or jar. For example, in some embodiments, the millingprocess may be stopped every about 30 minutes to evacuate gaseousby-products for safety reasons. In some embodiments, the process ofmilling may also be performed so as to avoid evaporation of solventssuch as water from the aqueous electrolyte solution. For example, themilling vessels or jars used in the milling processes may be kept at atemperature formulated to avoid evaporation of the solvents, such asroom temperature.

In some embodiments, the resulting products of the second milling step,which may appear brown and have a fluffy structure, may bepost-processed to at least remove extraneous by-products or residuessuch as but not limited to metallic ions, surfactants, metal salts,etc., e.g., step 106 of FIG. 1. For example, the product may be washedwith one or more of water, hydrochloric acid (HCl), ethanol, etc., andthe washing may be followed by vacuum filtration and vacuum drying. Theresulting final product of the two-step milling processes can be singleor thinned few layer graphene sheets that are highly electrostaticallycharged, hydroxylated and partially oxidized. For example, thesegraphene sheets can be partially oxidized graphene sheets withhydroxylated edges where at least some of the hydroxyls are convertedinto carbonyl molecules, which tend to be more active for bonding withother materials than the hydroxyl groups. In some embodiments, theportion of hydroxyl ions that convert into carbonyls may range fromabout 10% to about 40%, from about 15% to about 35%, from about 15% toabout 30%, about 20%, etc., of the hydroxyls. The conversion allowsgraphene sheets to exhibit enhanced dispersibility and mixability inboth polar and non-polar solvents, which results from electrons that arereleased in solvents such as water during the breaking of one of thedouble bonds that bind carbon and oxygen atoms in a carbonyl molecule.Accordingly, the final product shows good dispersibility and mixabilityin various matrixes such as polar solvents, non-polar solvents,polymers, and/or the like, for example.

In some embodiments, the disclosed two-step process can produce a largequantity of graphene sheets that are highly electrostatically charged,hydroxylated and partially oxidized in a single setting, representing ahigh yield of about 92% under certain conditions. In some embodiments,the yield may range from about 85% to about 95%.

At least some embodiments of the second step of the disclosed two-stepmilling process have been employed experimentally to treat the graphenesheets of the first stage of the two-step process as discussed herein.In some embodiments, the final graphene sheets of the two-step processfollowing the second stage can be conveniently classified into thefollowing class or grade:

-   -   Grade F: A highly activated few-layer graphene of about 2 to 3        graphene layers with at least some of the hydroxyl groups at the        edges of the graphene sheets have oxidized to form carbonyl        groups. Grade F can further be classified into grades F1 and F2        based on at least the lateral sizes of the graphene sheets,        and/or the ratio of carbonyl to hydroxyl attached to the edges        of the graphene sheets. Grade F1 usually have more carbonyls and        exhibit different properties than grade F2 graphene sheets. For        example, some of the graphene sheets can have a lateral size        (e.g., flake diameter) in the range of from about 0.1 μm to 0.2        μm (Grade F2) and 0.2 μm to 0.5 μm (Grade F1).

In some embodiments, Raman spectroscopy can be used to characterize theproperties of grade F graphene sheets such as thickness, defect density,etc. Using visible light (e.g., 532 nm wavelength light corresponding to2.33 eV energy), the Raman spectra for grade F FLG may be obtained asshown in FIG. 5, which shows the G, D and 2D peaks that are discussedabove with reference to with respect to grades A, B, C and D. Usingsimilar techniques described above for obtaining the thicknesses ofgrades A-D, the thicknesses of grade F graphene sheets may be determinedto be about 1 to 3 graphene layers.

Similarly, XPS may be used to characterize the surfaces and identify thehydroxyl groups attached to grade F graphene sheets, as shown in FIG.10F, where the aforementioned four intensity peaks can be identified,corresponding to peaks from carbon sp², carbon sp³, carbon-oxygen (C—O)and π-π bond. Integrals, i.e., summation of the intensities of each peakfor grade F is tabulated in Table 1 above, indicating that grade Fgraphene sheets comprise activated edges with hydroxyl groups.

TABLE 2 C1s sp3 C1s sp2 C1s C—O Cls C═O Graphite 16% 63% 21% 0%Electrostatically 11% 66% 23% 0% Charged Graphene Partially 16% 60% 19%3.94%   Oxidized Graphene

FIGS. 6A-6G show the deconvoluted XPS Carbon 1s spectra of Grade F. Themain difference from the other grades is the emergence of a new peakaround 287.5 eV that can be attributed to carbonyl, which is confirmedby the non-zero value for the integration of the peaks that indicates a3.94% presence of carbonyl groups (as shown in the table above, Table2), in contrast to the vanishing values for grades A-D. Hydroxyl groupquantification is lower in Grade F compared to Grades A to D, and it isnoticeable that the difference corresponds with the quantification ofcarbonyl groups, leading to the conclusion that some hydroxyl groupshave been oxidized to form carbonyl.

In some embodiments, FTIR measurements can provide additional supportingevidence as to the XPS detection of the presence of carbonyl groups onthe edges of grade F FLGs. For example, FIG. 14C shows the FTIR spectraof grade F FLGs where several significant absorption bands,corresponding to different local environments, can be identified:

-   -   around 1100 cm⁻¹ wavenumber, due to the stretching mode of        alkoxy C—O bonds,    -   around 1250 cm⁻¹ wavenumber, due to the epoxy C—O asymmetric        stretching vibrations,    -   around 1400 cm⁻¹ wavenumber, associated with the carboxy O—H        bonds,    -   around 1590 cm⁻¹ wavenumber, corresponding to C═C, from the        non-oxidized sp² carbon bonds,    -   around 1750 cm⁻¹ wavenumber, associated with C—O, stretching        vibrations,    -   around 3200 cm⁻¹ wavenumber, comprising contribution from the        adsorbed water molecules, and    -   around 3430 cm⁻¹ wavenumber associated with the O—H oscillations        in the carboxylic groups, on the edges of graphene planes, as        well as in between the graphene sheets.

These measurements show that carbonyl groups were added to the hydroxylgroups on the edges of the platelets, and in general provide furtherevidence of edge activation of the graphene sheets. FIG. 14 providesadditional example plot of XPS, TGA, and FTIR spectra of (partially)oxidized graphene, according to an embodiment.

In some embodiments, the thermal stability of the graphene sheets ofgrade F may also be investigated via a thermo gravimetric analysis (TGA)similar to as discussed above with reference to grades A-D. For example,a TGA analysis can be performed by raising the temperature of a furnacecontaining grade F graphene sheets and measuring the sample weight. FIG.12C shows the weight percentage of the sample remaining after mass lossas a function of temperature when the temperature is raised to 930° C.at a rate of 10° C./min rate in air. In the figure, two weight decreasescan be observed in the TGA data, where at around 250° C., structuralwater, hydroxyl and carbonyl groups are removed from the powder, and ataround 592° C., the decomposition of the graphene sheets occurs. Thisdecomposition temperature can be slightly lower than that for Grade Dbut still very close, showing that the pristine nature of the graphenesheets has been conserved during the milling processes. The results alsoshow the heat resistance properties of grade F graphene sheets.

Applications

The different grade graphene sheets and related composites producedaccording to the disclosed processes can be used to improve materialperformance across a wide range of industries. Addition of even a minuteamount of graphene-polymer composites can dramatically improve theproperties of base polymers to which the graphene materials are added,partly due to the dispersability of the low defect graphene sheets ofthe various grades. For example, a low graphene loading level rangingfrom about 0.05% to about 0.2% by weight may lead to significantperformance improvements. As a specific example, adding about 0.5 wt %of the disclosed graphene to PEI (Polyetherimide) may result inexcellent anti-corrosion coatings and adding just 0.2 wt % to siliconerubber may increase the thermal conductivity by almost 450%. Excellentimprovements in the properties of materials such as polylactic acid(PLA), polyethylene (PE), ultra-high-molecular-weight polyethylene(UHMWPE), Polyetherimide (PEI), acrylonitrile butadiene styrene (ABS),silicone rubber, etc., can also be achieved, such properties includingthermal conductivity, anti-corrosion and mechanical strength. Theability to achieve large performance improvements with very littlegraphene makes the graphene sheets economically viable for a largenumber of applications across a wide range of industries.

Some of the techniques that can be used to disperse graphene in multiplematrixes such as water and oil based lubricants or even polymerscomprise dispersing partially oxidized graphene in the ethanol initiallyand produce a master batch. In some embodiments, partially oxidizedgraphene may represent a fair dispersibility in water although itsstability may be limited to a few days. Further, partially oxidizedgraphene may represent a high dispersibility and stability in non-polarsolvents such as ethanol. For example, ethanol can act as a carrier forpartially oxidized graphene and improve the stability of such productsin the aqueous mediums. Adding a solution of partially oxidized grapheneinto lubricants can improve the lubricity of such liquids dramatically.For example, adding about 0.1 wt % of partially oxidized graphenedispersed in the ethanol into paraffin oils can reduce friction by about66%. As another example, dry adding partially oxidized graphene intosilicone rubbers can enhance the tensile strength dramatically whileimproving the hydrophobicity of the surface. Such products can havemultiple applications in the aerospace industry such as de-icing layersor as conductive paints for anti-lightening.

Lubricants

Graphene can provide significant benefits for lubricants in at leastthree ways, including as an additive to improve oil-based lubricants, asa replacement for existing, hazardous additives (e.g., for currentenvironmentally unfriendly lubricant additives such as molybdenumdisulfide or boric acid), and as a replacement for graphite-basedlubricants. As an additive, for example, adding graphene to existingoil-based lubricants provides many advantages including reducingfriction, forming an extremely strong and durable surface layer on thetarget surfaces that can be stable under a wide range of loads andtemperatures, improving lubricants to act as excellent cooling fluidremoving heat produced by friction or from external sources, andimproving lubricants to protect surfaces from the attack of aggressiveproducts formed during operation (including anti-corrosion protection).For example, a test by lubricant specialists of the graphene of thevarious grades has shown a very low loading of about 1 mg/mL in paraffinoil, the coefficient of friction was reduced by about 66%.

Graphite is a commonly used solid lubricant, especially in moist air(but may not protect the surface from corrosion). It has been shown thatgraphene works equally well in humid and dry environments. Furthermore,graphene is able to drastically reduce the wear rate and the coefficientof friction (COF) of steel. The marked reductions in friction and wearcan be attributed to the low shear and highly protective nature ofgraphene, which also prevents oxidation of the steel surfaces whenpresent at sliding contact interfaces.

Using the graphene-based products of the wet ball milling processesdisclosed herein as additives, even in minute amounts such as between1.0% and 0.1% of graphene by weight as an additive, the above-mentionedadvantages of graphene in lubricants can be realized. Further, theminute amount creates minimal or no impact to existing manufacturingprocesses, also allowing for a compact product development andintroduction timeline. The higher quality of the graphene-based productsallow for minute amounts to achieve significant improvements inlubricant performance, which partly is the result of the ability to tunethe dimensions of the graphene nanoplatelets and their dispersiveness inother materials. In some embodiments, it is useful to have the abilityto tune the dimensions of the graphene nanoplatelets depending on thetarget application. The dimensions can be lateral size (e.g.,diameter)—larger nanoplatelets generally provide more continuous surfaceprotection, and dispersion—smaller particles are often more easilydispersed in the target lubricant.

Coatings and Paints

Coatings are used to improve the surface properties of a substrate,properties such as corrosion resistance, durability, wettability, andadhesion. Paints are a special category of coating, used to protect,beautify and reduce maintenance requirements. Graphene, alone or as partof a composite, displays excellent characteristics for the coatingindustry including water and oil resistance, extraordinary barrierproperties (including anti-corrosion), superb frictional properties, andhigh wear resistance. In addition, graphene has excellent electrical andthermal properties and thin layers of graphene are opticallytransparent. Further, graphene based coatings exhibit excellentmechanical properties as well as being largely or completely impermeableto gases, liquids and strong chemicals. Examples include using graphenebased paint to cover glassware or copper plates that may be used ascontainers for strongly corrosive acids. Other areas of applicationsinclude industries in medicine, electronics, nuclear and shipbuilding,were identified. The graphene based products of the wet ball millingprocesses of this disclosure can be used to accomplish theaforementioned applications of graphene in as a coating additive.

Composite Materials

Composite materials are made from two or more different materials thatare combined together to create a new material with characteristicsdifferent from the individual components. The goal is to create asuperior new material with improved performance in some aspect such asstrength, less weight or lower cost. Graphene, with its unprecedentedarray of material characteristic improvements, is a natural candidatefor use in advanced composite materials. Leading candidates forgraphene-based composites include structural and skin components forairplanes, cars, boats and spacecraft. In these applications, graphenecan be used to increase thermal conductivity and dimensional stability,increase electrical conductivity, improve barrier properties, reducecomponent mass while maintaining or improving strength, increasestiffness and toughness (impact strength), improve surface appearance(scratch, stain and mark resistance), and increase flame resistance. Thegraphene based products including the graphene-graphite composite andthe edge activated FLGs discussed in this disclosure can be used justfor such applications. Examples of the effects of these products includeimproving mechanical/structural properties, thermal and/or electricalconductivity, wear resistance and long lasting surface properties,anti-corrosion and anti-erosion properties, particularly under dynamicloads; and electromagnetic shielding.

Experimental Demonstration of Effects of Grades of Graphene onMechanical Properties

Polymers can be highly adaptable and as such can be used in a wide rangeof challenging engineering applications, from composite wind turbineblades in the renewable energy sector to highly complex structural partsof aeroplanes. The incorporation of graphene in the polymer matrix canbe a highly effective way to improve the mechanical properties ofpolymers. Table 3 below shows an experimental demonstration of theimpact of grade F2 graphene additive powder on tensile strength andelongation at break in a commonly-used rubber compound consisting ofnatural and synthetic rubber. Mechanical properties were measuredaccording to American Society for Testing and Materials standard (ASTM)D412 (Standard Test methods for Vulcanized Rubber and ThermoplasticElastomers) with an Instron 3365 machine. The graphene-infused rubbersample was found to have a tensile strength of about 13 MPa which is anabout 11% improvement. The tensile strain at break also increased byabout 22.7% making the resultant material more ductile and flexible.

Tensile strength and strain at break were also evaluated for acrylatedmonomer base resins used for UV cured 3D printing materials. The purebase resin was mixed with graphene and cured. Traction dogbones werethen tested following ASTM D0638 standards, and a 57% increase intensile strength was observed in samples containing about 0.5% wtgraphene and the tensile strain at break almost doubled as well.

In some embodiments, toughness describes the ability of a material toabsorb energy and plastically deform without fracturing and it may be animportant material property for design applications. FIG. 16 shows anexample experimental demonstration of the effect of adding about 0.5 wt% of grade D graphene into UHMWPE (Ultra High Molecular WeightPolyethylene), which increased the toughness by about 40%. To achievecomparable enhancement with carbon nanotube (CNT) and nanoparticle epoxycomposites, one to two orders of magnitude loadings may be used.

Thermal Management

The demand for innovative thermal management materials and adhesives isdriven by the harmful heat generated by ever-shrinking electroniccomponents and systems in all areas of the electronics market, includingaerospace, automotive, consumer, communications, industrial, medical,and military. In recent years, there has been an increasing interest innew and advanced materials for thermal interface materials (TIM) andheat conduction. The important basic factors to consider when selectinga thermal interface material (TIM) are a high, thermally conductiveinterface material that is as thin as possible, a material that forms anexcellent thermal interface with a wide range of materials and amaterial that eliminates voids or air pockets between the heatgenerating device surface and the heat sink surface. The graphene basedproducts disclosed in this disclosure possess superior electricalconductivity, and ultra-low interfacial thermal resistance againstmetal, and as such are suitable for thermal management applications.Further, the edge activation facilitates mixing with other materialssuch as existing TIM materials. As such, for example, they can be usedin producing thermally conductive polymer composites that can provideopportunities to form complex, light weight, three-dimensional andeco-friendly objects and devices. For example, thermally conductivepolymer composites can be used to produce microelectronic enclosures,passive heat sinks with complex shapes, novel electrical motor casings,and/or the like with superior heat dissipation performance.

Experimental Demonstration of Effects of Grades of Graphene on ThermalProperties

In some embodiments, a Modified Transient Plane Source (MTPS) techniquethat employs a one-sided, interfacial heat reflectance sensor to apply amomentary constant heat source can be used to measure thermal properties(e.g., conductivity) of polymer materials. For example, thermalconductivity and effusivity can be measured directly using such atechnique, providing for a detailed profile of the thermalcharacteristics of the samples being measured. Table 1 below shows anexperimental demonstration of the significant impact on the thermalconductivity of different polymers that can be obtained by usinggraphene sheets of the various grades. As an example, the thermalconductivity of PLA can be increased by approximately 250% with theaddition of about 0.075 wt % of grade F2 graphene.

TABLE 4 Thermal Conductivity at Improved Thermal Improved 21-25° C.Thermal Effusivity Thermal Material (W/mK) conductivity (Ws^(0.5)/m²K)Effusivity PLA* 0.36 245%  714 112%  PLA + 0.075 wt % Graphene 1.23 1517Grade F2 PE** 0.74 44% 888 55% PE + 0.1 wt % Graphene 1.06 1377 Grade DABS*** 0.29 339%  643 142%  ABS + 0.05 wt % Graphene 1.28 1555 Grade F2Silicone rubber 0.23 446%  572 166%  Silicone rubber + [0.1 wt % 1.241522 Graphene Grade F1 + 0.1 wt % Graphene Grade F2] 2-part epoxypotting 0.38 45% 771 17% compound 2-part epoxy potting 0.55 905compound + 0.075 wt % Graphene Grade SD Silicone heat transfer 0.66 54%1190 15% compound Silicone heat transfer 1.02 1367 compound + 0.1 wt %Graphene Grade D Polyurethane 0.21 80% 550 33% Polyurethane + 0.13 wt %0.37 730 Grade F2

As discussed above, graphene sheets produced using the processesdisclosed herein significantly improve the thermal properties ofpolymers the graphene sheets are mixed with, especially in comparison tographitic materials produced using other processes. Table 2 provides anexample of such an effect with respect to graphene/PLA conductivethermoplastic polymer.

TABLE 5 Graphene produced by the Graphene not produced by disclosed twostep milling the disclosed two step processes milling processes Loadinglevel of graphene 0.075 wt % 10-15 wt % Improvement in thermal 245%40-50% conductivity

In some embodiments, there may be an optimum range and/or value ofgraphene amount that can be mixed with a material so as to produce acomposite with desired enhanced properties. For example, for any targetpolymer, one or more of the aforementioned graphene grades can be mixedat very small concentrations (usually around 0.1% by weight) to improveintrinsic heat dissipation properties of the polymer. In someembodiments, the concentration of graphene can be finely tuned so as todiscover an optimal value that achieves the desired properties (e.g.,highest thermal conductivity). FIG. 15 shows an example embodiment ofthe determination of an optimal concentration of graphene for PLA andABS. For example, in the case of PLA, the optimal graphene concentrationis about 0.075% by weight.

Energy

Graphene-based nanomaterials have many promising applications inenergy-related areas. Graphene improves both energy capacity and chargerate in rechargeable batteries; graphene makes superior supercapacitorsfor energy storage; transparent and flexible graphene electrodes maylead to a promising approach for making solar cells that areinexpensive, lightweight and manufactured using roll-to-roll techniques;graphene substrates show great promise for catalytic systems in hydrogenstorage for automotive and grid storage applications.

The graphene based products of the present disclosure can beparticularly suited to electrode-based energy solutions, andspecifically for improving the performance of Li-ion anodes. CurrentLi-ion anodes are made from graphite while new generation anodes arebeing fabricated from composites such as silicon-carbon. Graphenecomposite anodes, fabricated using a composite of graphene and metals,oxides or polymers, can have even better performance in the areas ofpower density, energy density, and battery cycle life. Further, graphenebased composites can often provide production advantages while alsohelping to address the overheating and swelling problems oftenexperienced by advanced battery cells. In addition, the excellentthermal and electrical conductivity, and the ability to mix and formcomposites with a wide range of other materials, of the graphene basedproducts of the present disclosure allow for its use in batterytechnologies, including effecting improvements in the performance ofLi-ion batteries.

While various embodiments of the system, methods and devices have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Where methods and stepsdescribed above indicate certain events occurring in certain order,those of ordinary skill in the art having the benefit of this disclosurewould recognize that the ordering of certain steps may be modified andsuch modification are in accordance with the variations of theinvention. For example, the non-aqueous electrolyte can also include agel polymer electrolyte. Additionally, certain of the steps may beperformed concurrently in a parallel process when possible, as well asperformed sequentially as described above. The embodiments have beenparticularly shown and described, but it will be understood that variouschanges in form and details may be made.

1.-174. (canceled)
 175. A method for producing functionalized graphene,comprising: transferring graphite into a milling vessel, the graphitehaving a first aspect ratio; transferring a solvent into the millingvessel; transferring a surfactant into the milling vessel; transferringa first oxidizing agent into the milling vessel; transferring a secondoxidizing agent into the milling vessel; and milling the graphite in thepresence of the solvent, the surfactant, the first oxidizing agent, andthe second oxidizing agent to produce functionalized graphene, thefunctionalized graphene having a second aspect ratio, the second aspectratio larger than the first aspect ratio.
 176. The method of claim 175,wherein the solvent includes water.
 177. The method of claim 175,wherein the first oxidizing agent includes a metal hydroxide salt. 178.The method of claim 177, wherein the metal hydroxide salt includespotassium hydroxide.
 179. The method of claim 175, wherein the firstoxidizing agent has an oxidation potential greater than about 1.5V. 180.The method of claim 175, wherein the first oxidizing agent has anoxidation potential less than about 1.5V.
 181. The method of claim 175,wherein the functionalized graphene is hydroxylated.
 182. The method ofclaim 181, further comprising: converting a hydroxyl group of thefunctionalized graphene to a carbonyl group.
 183. The method of claim175, wherein the functionalized graphene is carbonylated.
 184. Themethod of claim 175, wherein the functionalized graphene is few layergraphene.
 185. The method of claim 175, further comprising: isolatingthe functionalized graphene; washing the functionalized graphene; andfiltering and drying the functionalized graphene.
 186. The method ofclaim 175, wherein the second oxidizing agent includes a peroxide. 187.A method, comprising: transferring graphite into a milling vessel, thegraphite having a first thickness, the milling vessel including a media;transferring a solvent into the milling vessel; transferring asurfactant into the milling vessel; transferring a metal hydroxide saltto the milling vessel; transferring an oxidizing agent into the millingvessel; and rotating the milling vessel in the presence of the solvent,the surfactant, the metal hydroxide salt, and the oxidizing agent toproduce functionalized graphene, the functionalized graphene having asecond thickness, the second thickness smaller than the first thickness.188. The method of claim 187, wherein the solvent includes water. 189.The method of claim 187, wherein the oxidizing agent is at least one ofa peroxide, a chromate, a chlorate, or a perchlorate.
 190. The method ofclaim 189, wherein the oxidizing agent is hydrogen peroxide.
 191. Themethod of claim 187, wherein the functionalized graphene ishydroxylated.
 192. The method of claim 191, further comprising:converting a hydroxyl group of the functionalized graphene to a carbonylgroup.
 193. The method of claim 187, wherein the oxidizing agent has anoxidation potential less than about 1.5V.
 194. The method of claim 187,wherein the functionalized graphene is carbonylated.
 195. The method ofclaim 187, wherein the functionalized graphene is few layer graphene.196. The method of claim 187, further comprising: isolating thefunctionalized graphene; washing the functionalized graphene; andfiltering and drying the functionalized graphene.